The present invention relates to transmission units for automotive vehicles, and more particularly to a final speed-reduction gearing assembly suitable for an automatic transmission unit adapted to an internal combustion engine of the transversely mounting type.
As is illustrated in FIG. 1, such a conventional final speed-reduction gearing assembly as described above is mounted within a trans-axle casing 16 in which an output drive pinion shaft 10 is drivingly connected to a torque converter assembly 12 through a planetary gearing unit 14. The final speed-reduction gearing assembly includes a ring gear 18 in mesh with a drive pinion 11 integral with shaft 10, and a differential gear unit 20 integrally connected at its outer case 22 with ring gear 18, the outer case 22 being provided at its opposite ends with a pair of cylindrical sleevelike side-journals rotatably supported by a pair of axially spaced tapered roller bearings 26, 28 which are respectively mounted on a carrier portion A of a retainer case 24 detachably fixed to trans-axle casing 16 and a carrier portion B of trans-axle casing 16. For adjustment of a preload axially acting on tapered roller bearings 26, 28, a pair of annular shim plates 30, 30 are disposed respectively between the outer end of bearing 26 and the inner end wall of carrier portion A and between the outer end of bearing 28 and the inner end wall of carrier portion B.
In the foregoing arrangement, the final speed-reduction gearing assembly is designed to be inserted into and removed from trans-axle casing 16 through an opening 17 located at the rear side of casing 16, which is closed by a cover member 32, and after adjustment of the preload acting on tapered roller bearings 26, 28, a pair of axle shafts 34, 36 are assembled with a pair of side gears of the differential gear unit 20. In this type of final speed-reduction gearing assemblies, it is advantageous that the differential gear unit 20 can be removed from trans-axle casing 16 only by removing the cover member 32 to be disassembled for repair. It is also advantageous that the opposite ends of drive pinion shaft 10 are precisely supported in place because the trans-axle casing 16 is integrally constructed to enhance rigidity of casing 16 in comparison with that of a casing of the split type. On the other hand, it is, however, noted that in adjustment of the preload acting on tapered roller bearings 26, 28, the retainer case 24 and the differential gear unit 20 must be removed from trans-axle casing 16 and subsequently the roller bearings 26, 28 must be removed for replacement of the annular shim plates 30, 30. This results in time consumption for adjustment of the preload acting on the roller bearings and results in damage of the carrier portions A and B due to abutment against the component parts of differential gear unit 20 during the removing and assembling processes of unit 20.